Method of treatment of pyritic materials



Dec. 29, 1936.,

C. R. ARNOLD ET AL Filed Oct. 20, 1934 2 Sheets-Sheet '1 coucsmizm's COAL Oxides of Sulphur mlxms MILL SODIUM SULPHURIC pRgsacEk N'TRATE STORAGE v k Concenfrafe Mlxfure I v SULPHURIO SulphuricAoid f fifg'fi REDUCING w ,FURNACE Heal Poasfed Concenfrafe Wafer V Oxides of SULPHIDE GAS 571/ hur BURNER STEAM fiulnh uric Acid BOILER Hydrogen Sula/"d8 Gas Mofher L/ Jar 1: L 4 Sfeam DIGESTOR Wffl'gr u Iran Sula/ml? a-Res/aue V Wash Iran 541/ gate LI 0/- HLTER Wafe r w CRYSTALLIZER ream Solid Residue Iron 511/ ale C fats 0 5 GOLD-BEARING i of Sup/7a ROAS'HNG He RESIDUE FURNACE 4 1 Water Ferric Oxide T PREPARED- FDR J AMALGAMATION WET MILL u w Slurr 0fFerr/c0x/de Res'due a M ROASTING J FURNACE M Roasfea' Residue 35am somsa'nme Rasmue Oxides or suflghur PREPARED FOR FERRIC OXIDE CYANIDING CHLORINATION OR AMALGAMATION BY Fm C. R ARNOLD ET AL Filed Oct. 20, 1934 Oxides of Sulphur 2 'SheetsSheet 2 V COAL MIXING MILL $ODIUM kgfg I eAs NITRATE: R ouce WAGE ConcenirafeMx/ure I I I I; auLPIIuRIc sul huricAcid AIR I t 3:33 SUBLIMATION REDUCING s CHAMBER FURNACE I m I earn Oxides of SULPHIDE GAS I SULPH'DES 0F Roasted concenfmfe M I BURNER ARSENIC S ANTMONY STEAM u/ A 5 I Sulphuric Acid wLE I v V 4 Hydrogen Sulphizie Gas aulphafe Moiher Liquor-s M 5u/p/1ae Lieuor feam IL 5 DIGESTOR Wafer V II 5mm *1 Sulphafes likes/due Hot n or sfals 5 LT FILTER x, h asses 5 CRYSTALLIZER EPARATOR COPPER Oxides of Sidebar Oxides of su/ hJI- Wafer Wafer Iron Sulphafe Crysfa/s ROASTING FURNACE WET MILL FILTER DRYER Ferric Oxide Slurr of Ferric Oxide Ferric Oxide Cake FERRIC OXIDE Solid Residue I GOLD-BEARING REIDUE' PREPARED FOR AIIMLGAMATION Solid Residue Roasfed Residue ROATING FURNACE GOLD-BEARING RBSIDUE map/man FOR CYAhgDlNG, cIILoRINAnoII R AMAUSAMATION IINVENTOR ATTORNEY4 Patented Dec. 29, 193

PATENT OFFICE I METHOD OF TREATMENT OF PYRITIC MATERIALS 7 Craig It. Arnold, Dahlonega, Ga., and

- Frank N. Moerk, Philadelphla, Pa.

Application October so, 1934, Serial No. 749,264

colaims. (01.75-83) This invention is a method of treatment of pyritic materials, such as pyritic ores, concentrates and the like, functioning advantageously for recovering useful ingredients from gold bearing ore, and while it applies particularly to. methods for treatment of gold-bearing pyritic ores,

concentrates and the like, it may be employed with other ores, concentrates and the like, as will be understood by those skilled in the art;

10 It is a known fact that many ore deposits contain gold, but those deposits have never been mined because the cost'of extracting the gold has exceeded the value of the gold when extracted. The objects of the present invention are to pro- 55 vide a method of extracting gold upon a comsimplicity in the can'ying out of the process; and

5 to obtain other advantages and results as may be brought out in the following discussion.

, For assisting in the better understanding of the invention and the cycle of operations embodied therein, we supply herewith a drawing which dia-.

grammatically indicates the various pieces of apparatus employed and their relationship in the process together with anindication of the materials employed and disposition made thereof in the cycle of operations. This drawing represents what is ordinarily referred to in the art as a flow sheet. The drawings comprise two figures, wherein Fig. 1 represents the flow sheet for extraction of gold and by-products from a pyritic ore of the more commonly found iron pyrites, and

Fig. 2, represents a flow sheet forore containing copper pyrite, the sulphides of copper, iron antimony, arsenic, and the like in desirable quantitles.

Broadly speaking, the method is one to facili- 45 tate the recovery of gold. and valuable by products from gold-bearing pyritic ores and concentrates by decomposing the pyrites and separating the iron and sulphur. whereby a residue is obknown processes and the iron converted into a useful by-product. Preferably the ore or concentrate-is ground toa satisfactory fineness, preferably such thatit will pass through a. sixty mesh 55 screen, and then is roastedflunder conditions tained from which .the gold may be recovered byever, before roasting, to mix the concentrate with a reducing agent, such as charcoal, coal, or carbonaceous matter, and to conduct the roasting in such manner as to preclude oxidation of the iron, either ingan intermittent or in a. continuous fur- 5 nace at a temperature sufllcient to' convert the pyrites into metallic sulphides, such as iron sulphide, arsenic sulphide, antimony sulphide, copper sulphide, and so forth. As indicated in Fig. 2, some of these sulphides, such as those of arsenic and antimony may be obtained by sublimation from the gases produced in the reducing furnace; Insofar as the roasting is effected at a temperature sumcient to convert the pyrites into metallic sulphides, and since the. operation is performed to preclude oxidation of the iron, the sulphur is likewise not oxidized until the fumes issue from the furnace and come in contact with air, the admission of air being provided for, as shown, as the gas leaves the furnace. The sulphur fumes are allowed to oxidize after leaving the furnace and are savedfor use in connection with the production of sulphuric acid.

tible and maybe burned with air to form water vapor and the oxides of sulphur, and returned to the cycle for use in the sulphuric acid plant. When the digestion is completed the mass is filtered and washed to separate the ferrous sulphate from the residue which contains the gold. The separationof the ferrous sulphate from. the goldbearing residue maybe effected by sedimentation and decantation if desired instead of resorting to 40 filtration, although filtration is to be preferred. The gold-bearing residue obtained at this point of the description is in such condition as to permit of the extraction ofthe major portion,

if not all, of its gold content by the well known -process of amalgamation with metallic mercury.

However, it has been found that in the digestion operation sulphur may be precipitated, probably as the result of the action of the acid on the dissolved hydrogen sulphide or because. of the reduction of the sulphuric acid. Since the presence of sulphur and organic or carbonaceous matters interferes with the etllcacy cf the gold extraction both by cyaniding and by chlorination, and increases the expense thereof, it is desirable acid plant into sulphuric acid. The'sublim 6 intoits oxides and returned to the sulphuric acid plant. After this step in the process, the gold may be extracted in suitable manner as by cyanlding, by chlorination, by amalgamation, or by other desired process.

10 The by-product value of the iron content of the ore or concentrate may be increased by conversion of the resultant ferrous sulphate crystals into the more valuable ferric oxide. It is accordingly an-important feature of the present invention' to convert the ferrous sulphate into ferric oxide. Concentration by recirculation, evaporation and crystallization of the ferrous sulphate solution indicated in the drawings yields crystals of ferrous sulphate, and it is these crystals that are next converted into ferric oxide. This result is accomplished by roasting the crystals at a temperature sufficiently high to drive off the water of crystallization and to liberate the oxides of sulphur. The resultant residue is a ferric oxide which may then be prepared for market by grinding in water and recovering the oxide by sedimentation or by filtration, thereafter drying the same when it is ready for disposition. The roasting temperature employed is important in that various shades of the oxide may be obtained which range from vermillion to deep purplishbrown, depending upon the roasting temperature. In event the pyrites have a considerable amount of copper sulphides, the first acid digestion of the roasted mixture of ore contains copper sulphate in addition to the ferrous sulphate. These sulphates may be separated upon concentration by fractional crystallization, or by heating the solution under pressure properly balanced to cause, the ferrous sulphate to crystallize or separate! while the copper sulphate remains in solution. After the removal of the ferrous sulphate crystals, the copper sulphate is crystallized and is a desirable icy-product of the process.

5 In the case of gold-bearing arsenical and antimonial pyritic ores the volatile products evolved upon'roasting under the reducing conditions tofore described are mixed with air as they issue from the furnace or retort to convert the sulphur o fumes into oxides of sulphur and are passed through a subliming chamber in which the sulphides and any oxides of arsenic and antimony collect, while the oxides ,of sulphur. pass through the chamber and are converted at the sulphuric ation points or temperatures of the sulphides of arsenic and antimony differ, and by controlling the temperatures in. the sublimation chamber or chambers a separation of the sulphides may be effect- 00 ed, or if the temperature is such that simultaneous sublimation occurs, the sulphides may I be later separated by chemical means.

For gold-bearing or'es containing any or all, or any combination of ingredients specified in the foregoing, corresponding portions of the \processes above described may be included for obtaining the desired products and by-products,

. It is to be understood that according to the pres- Y ent'invention the quantity of sulphuric acid depends upon the volatile sulphur content of the I ores, upon the amounts of ferrous sulphate converted into ferric oxide, and upon the amount of sulphur precipitated during digestion and volatilized during the roasting of the gold-bear- 75 ing residue. In some cases it may be in excess of 2 a a,oes,e47

re-x

the demands of the process, while in others it may be necessary to employ additional acid. However, the sulphuric acid is a valuable byproduct that is produced by and utilized in the' process. Furthermore, by the process disclosed 5 the gases evolved, particularly the obnoxious oxide are kept. within the cycle. of operations gases such as hydrogen sulphide and sulphur dirather thanbeing liberated to the atmosphere. The hydrogen sulphide gas from the digestion 10 operation may be burned with air to thus obtain a conversion into oxides of sulphur, which in that form is then usable in the production of sulphuric acid. This scheme accordingly converts otherwise offensive gaseous products into a ma- 15' terial of value which is needed in this method of treatment of pyritic ores and concentrates.

Obviously, as indicated above, portions of the process may be employed omitting other portions;

and the invention contemplates not'only the 0 complete combination of steps herein described in full, but contemplates subcombinations thereof and various combinations of the portions thereof andwe accordingly do not wish to confine ourselves to the steps described eitherin 25 the order given or necessarily inclusive of all of the said steps, except as set forth in the following claims when. construed in the light of the priorart.

The invention may be applied, in carrying out 30 the foregoing disclosure, to treatment of a goldbearing pyritic concentrate, containing, by way of example, 65% iron pyrites and assaying 0.462 ounces of gold per ton. Following the flow sheet of Figure 1, six parts of concentrate may be 35 mixed with one part of coal, ground to 'a fineness of -mesh, and roasted at a temperature between 1300 F. and 1500 F. in a continuous rotating tube furnace to decompose. the pyrites. The roasted product, which amounts to substantially 4 4.67 parts, may-now be made into a thin slurry with water to which 6 parts of 60 Baum sulphuric acid is added, and the mass digested at a temperature Just below the boiling point in order to convert the ferrous sulphide. content. into 45 ferrous sulphate. of. which 8.9 parts or thereabouts, should be obtained. upon filtration and crystallization. These crystals are, by roasting at a temperature of approximately 1300* F., converted into substantially 2.28 parts of ferric 5o oxide. The dried residue from the digestionoperation, which contains substantially all of the gold present in the original concentrate, will yield, according to this example, approximately gold extraction by chlorination or by cyaniding. a

and is not at all necessary when amalgamation is to be used to extractthe gold.

During the treatment of the above concentrate,-

, sulphur gases are evolved from the several roasting operations and from'the acid digestion op- 7 eratioh which amount to the equivalent of 5.8 parts of sulphur dioxide for every 6 parts of the concentrate. These gases are convertible into sulphuric'acid by the lead chamber process after passingthrou h a dust-removing chamber to remove the suspended particles. -With a emcient lead chamber process, nearly twice the amount of sulphuric acid required for our treating process will be produced.

We claim: I

1. The method of treating gold-bearing ores or concentrates, comprising roasting the ore or concentrate under reducing conditions, converting the liberated sulphur gases into sulphuric acid, digesting the roasted product with sulphuric acid, recoveringferrous sulphate from the digestion liquor, roasting the digested product under oxidizing conditions, and recovering the gold from the digested and roasted residue. 4

2. The method of treating gold-bearing ores or concentrates, comprising roasting the ore or concentrate under reducing conditions, converting the liberated sulphur gases into sulphuric acid, digesting the roasted product with sulphuric acid, recovering ferrous sulphate from the diges-..

tion liquor and converting it into ferric oxide, roasting the digested product under oxidizing conditions, converting the ox des of sulphur into sulphuric acid, and recoveringthe gold from the digested and roasted residue.

3. The method of treating gold-bearing ores and concentrates, comprising roasting the ore or concentrate under reducing conditions,-converting the liberated sulphur gases into sulphuric acid, digesting the roasted product with sulphuric acid, recovering and separating the sulphates of iron and copper from the digestion liquor, con-.

verting the ferrous sulphate into ferric oxide, and

recovering the gold from the digested residue.

4. The method of treating gold-bearing ore and/or concentrates, comprising roasting the ore or concentrate under reducing conditions, separating the volatile sulphides from the sulphur gases, converting the sulphur gases into sul phuric acid, digesting the roasted product with sulphuric acid, converting the evolved hydrogen sulphide gas into sulphuric acid, recovering and separating the crystals of ferrous and copper sulphates from the digestion liquor, converting the ferrous sulphate into ferric oxide and recovering the oxides of sulphur therefrom for conversion into sulphuric acid, and extracting the gold from the digested residue.

5. The method of treating gold-bearing ore and/or concentrates, comprising roasting the ore or concentrate under reducing conditions, separating the volatile sulphides from thesulphu'r gases, converting the sulphur gases into sulphuric acid, digesting the roasted product with sulphuric acid, converting the evolved hydrogen sulphide gasinto sulphuric acid, recovering and separating the crystals of ferrous and copper sulphates from the digestion liquor, converting the ferrous sulphate into ferric oxide and recovering the oxides of sulphur therefrom for conversion into sulphuric acid, roasting the digestion residue under oxidizing conditions to remove the interfering sulphur or carbonaceous matter and extracting the gold from the digested residue.

6. The method of treating pyritic ores and/or concentrates, comprising roasting the ore or concentrate under reducing conditions, separating the volatile sulphides from the oxidized sulphur gases, converting the oxidized sulphur gases into sulphuric acid, digesting the roasted product with sulphuric acid, converting the evolved hydrogen sulphide into sulphuric acid, converting the ferrous sulphate in the remaining product into ferric oxide, and recovering oxides of sulphur resultant from the last-mentioned con- 1 version, and converting the last-mentioned oxides of sulphur into sulphuric acid;

CRAIG R, ARNOLD. FRANK N. MOERK.

CERTIFICATE or CORRECTION.

Patent No. 2,065,547.. I December 29, 193s CRAIG R. ARNOLD, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, line 8, strike out the words and syllable "gases such as hydrogen sulphide and sulphur di-" and insert 'the same after "obnoxious" in line 6; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Offioe.

Signed and sealed this 24th day' of-August, A D. 1937.

Leslie Frazer (Seal) Acting Commissioner of Patents. 

